The proposed research seeks to elucidate the biochemical steps in the head assembly of bacteriophage lambda. Emphasis is placed upon understanding the properties and the roles of two protein processing reactions -- a protein fusion reaction and a proteolytic cleavage. The product of the fusion reaction will be isolated and characterized. The nature of an apparent shape change in head structures which accompanies the fusion reaction will be investigated. Specific antibodies will be used to attempt to determine the location of various proteins on the lambda virion, in particular the proteins that are involved in the processing reactions. Experiments will also be carried out to determine the nature of the precurssors to lambda heads and to investigate the possible membrane association of these precursors. Since direct host participation is known to be required for completion of either protein processing reaction, all of these studies will be concerned with the question of how the host is involved in virus maturation.